Rotation angle detector

Details Rotation angle detector Rotation angle detector

2002-01-23

2003-10-07

Patidar, Jay (Department: 2862)

Electricity: measuring and testing

Magnetic

Displacement

C324S207210

Reexamination Certificate

active

06630823

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a rotation-angle detector for detecting a rotation angle of, e.g., a steering shaft of a car.
BACKGROUND OF THE INVENTION
Recently, cars have been provided with a variety of functions and various controls are thus required. For that purpose, cars are equipped with rotation-angle detectors car for detecting a rotation angle of the steering shaft.
A conventional rotation-angle detector is described hereinafter with reference to FIG.
11
through FIG.
14
B.
FIG. 11
is a perspective view of a conventional rotation-angle detector.
FIG. 12
is a sectional view of the detector shown in FIG.
11
.
FIGS. 13A and 13B
show voltage-waveforms with respect to a rotation angle detected by the detector shown in FIG.
11
.
FIGS. 14A and 14B
show enlarged voltage-waveforms shown in
FIGS. 13A and 13B
.
In FIG.
11
and
FIG. 12
, rotary body
501
, on whose rim rotary-gear
511
is formed, engages first detecting gear
502
and second detecting gear
503
, and gears
502
and
503
have different numbers of cogs.
The numbers of cogs of gears
502
and
503
are set such that the numbers have periodicity with respect to a given rotation-angle of rotary body
501
. In other words, when rotary body
501
rotates twice counterclockwise or clockwise from a null position, rotary body
501
is to return to an original engaging relation at the null position.
Inside the rim of rotary body
501
, two engaging sections
512
are provided for engaging the steering shaft (not shown) extending through the center of rotary body
501
. Gears
502
and
503
have magnets
504
and
505
at their centers.
Circuit-board
506
is placed above gears
502
and
503
, and board
506
is equipped with first angle-sensor
507
and second angle-sensor
508
facing, respectively, the centers of gear
502
and gear
503
. Further, board
506
has detecting circuit
509
comprising a micro-processor for processing detection signals supplied from sensors
507
and
508
.
An operation of the rotation-angle detector discussed above is described hereinafter. In
FIG. 11
, when the steering shaft rotates, the torque is transmitted to rotary body
501
via the two engaging sections
512
, so that rotary gear
511
rotates. The rotation of gear
511
causes gears
502
and
503
engaged with gear
511
to rotate, respectively. At this time, sensors
507
and
508
detect magnetism from magnets
504
and
505
, whereby the rotation angles of gears
502
and
503
are detected.
Detection signals detected by sensors
507
and
508
are shown in
FIGS. 13A and 13B
. Since gears
502
and
503
have different numbers of cogs, the detection signals draw voltage-waveforms having rather different phases from each other with respect to their rotation angles while rotary body
501
rotates twice either clockwise or counterclockwise.
As the enlarged voltage-waveform in
FIG. 14
shows, detecting circuit
509
detects voltages of sensors
507
and
508
(i.e., they are the detection signals) and calculates the voltages as well as the numbers of cogs of gears
502
and
503
, so that rotation angle &thgr; of rotary body
501
is detected.
However, the conventional detector discussed above has encountered the following problems:
(a) The rotation angle of rotary body
501
is detected based on detecting the rotations of detection gears
502
and
503
engaged with rotary gear
511
. Therefore, gaps between gears
511
and
502
, as well as gaps between gears
511
and
503
, and looseness due to these gaps cause an error in detecting an angle, particularly when the gears start rotating or rotate in a reverse direction.
(b) Detecting a rotation angle requires complicated calculations by detecting circuit
509
.
(c) When a large rotation angle is detected, respective gears
511
,
502
and
503
need to have greater numbers of cogs due to a periodic relationship between gear
511
and gears
502
,
503
. As a result, larger diameters are necessary, which prevents the entire detector from being downsized.
SUMMARY OF THE INVENTION
The present invention addresses the problems discussed above, and aims to provide a downsized rotation-angle detector that produces a smaller detection error, and a simpler calculation is carried out in a detecting circuit thereof.
The rotation-angle detector of the present invention comprises the following elements: a rotary body having a rotary gear; a change gear engaged with the rotary gear; a driven body moving following the rotation of the change gear, a first detector for detecting a movement of the driven body; a detecting gear engaged with the change gear; a second detector for detecting a rotation of the detecting gear; and a detecting circuit for processing detection signals supplied from the first and the second detectors. The first detector detects the movement of the driven body as a first detection signal gradually increasing or decreasing, and the second detector detects the rotation of the detecting gear as a second detection signal repeating continuously. The detecting circuit detects a rotation angle of the rotary body based on the two detection signals. This structure allows the detector of the present invention to produce a smaller error, be downsized, and make simple calculation in the detecting circuit.


REFERENCES:
patent: 5146173 (1992-09-01), Jurkewitz
patent: 5930905 (1999-08-01), Zabler et al.
patent: 6507188 (2003-01-01), Dilger et al.
patent: 1 018 466 (2000-07-01), None
patent: 1 093 993 (2001-04-01), None
patent: 1 108 987 (2001-06-01), None

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